This invention relates to a new chemical synthesis of 1,1,1-trimethyl-N-sulfinyl silanamine, (CH.sub.3).sub.3 SiNSO. It also relates to other uses of the same reaction and its byproducts.
(CH.sub.3).sub.3 SiNSO is of great interest in the organosilicon industry. It is used in the synthesis of selected heterocycles, symmetric disulfides, and other sulfinylamines. It would be desirable to manufacture this compound by a simple and direct method with a rapid reaction rate and high yields. The compound was first synthesized by the reaction of tris(trimethylsilyl)amine with thionyl chloride at 70.degree. C. in the presence of aluminum chloride catalyst. Other synthetic routes have since been reported in the chemical literature, such as the reaction of (C.sub.6 H.sub.5)SNSO with (CH.sub.3).sub.3 SiS(C.sub.6 H.sub.5) to produce the product of interest plus (C.sub.6 H.sub.5).sub.2 S.sub.2, and the reaction of (n-C.sub.4 H.sub.9).sub.3 SnNSO with covalent chlorides such as (CH.sub.3).sub.3 SiCl, to produce (CH.sub.3).sub.3 SiNSO and (n-C.sub.4 H.sub.9).sub.3 SnCl. These synthetic routes are ill-suited to large-scale industrial production of the compound because they require exotic and expensive starting reagents and give unsatisfactory yields.
A method has been developed for the production of (CH.sub.3).sub.3 SiNSO involving the direct reaction of SO.sub.2 with a common silylating agent. The starting materials are relatively inexpensive, and the reaction proceeds to 100% completion at ambient temperatures.
In addition to providing a new and novel method for producing (CH.sub.3).sub.3 SiNSO, the same reaction may be used in a different way to measure the concentration of SO.sub.2 in gases such as industrial stack gases or ambient air. SO.sub.2 is a major air pollutant. Frequently, the quantity of SO.sub.2 being released into the air must be monitored, particularly in an industrial setting. Several methods are currently being used for this purpose, including wet chemical and electroanalytical methods, H.sub.2 flame photometry, and fluorescence. Wet chemical and electro-analytical techniques are often slow and their systems require frequent maintenance. H.sub.2 flame photometry is unsatisfactory because the high flammability of H.sub.2 is a major safety hazard and because other sulfur compounds may act as interferences. Techniques which measure the fluorescence of the SO.sub.2 itself are subject to interference from other atmospheric oxides and hydrocarbons. It would be desirable to have a method for SO.sub.2 analysis which would allow samples to be taken at remote sites far from the analytical laboratory. Ideally, the method would be reliable and simple to use. It would be highly specific, free of most interferences, accurate, and would require relatively inexpensive apparatus.
The reaction of the subject invention combines SO.sub.2 and a common silylating agent to produce (CH.sub.3).sub.3 SiNSO and [NH.sub.4 ][(CH.sub.3).sub.3 SiOSO.sub.2 ]. Both of these compounds have fluorescent properties. This reaction may be used to determine SO.sub.2 conveniently and reliably in gases such as ambient air or industrial stack gases by passing a sample of the gas through the silylating agent to react any SO.sub.2 in the gas with the silylating agent, exciting the reaction products to induce fluorescence, and measuring the fluorescence produced, the fluorescence of the the products being determinative of the quantity of SO.sub.2 in the original gas sample.
In addition to these uses, the reaction of the subject invention also produces the new by-product [NH.sub.4 ][(CH.sub.3).sub.3 SiOSO.sub.2 ]. This compound has a new and unexpected use in the field of nuclear magnetic resonance spectroscopy (NMR). NMR is a well established tool for investigating the structure of molecules in the liquid state. It is increasingly being used to study molecular structures in the solid state. These studies have been hindered by the lack of a solid state standard from which to measure chemical shift data. Such a standard should be chemically inert, magnetically isotropic, and volatile. It should give a single sharp absorption line and it should absorb at a frequency higher than that of the samples to be measured. The new compound produced by the reaction of the subject invention has many of these properties and is a convenient standard for solid state NMR spectroscopy.